F.M. Liu

Investigation of surface-enhanced Raman scattering from platinum electrodes using a confocal Raman microscope: dependence of surface roughening pretreatment

Abstract In order to establish an appropriate surface roughening procedure for obtaining high-quality surface Raman spectra from Pt electrodes, various roughening conditions for the SERS from the adsorbed pyridine, thiocynate and hydrogen are assessed in terms of the corresponding surface Raman intensities, enhancement factors and surface homogeneity. The repetitive square-wave oxidation reduction cycle (SWORC), triangular-wave ORC (TWORC) and platinization have been performed in the present study. The enhancement factor ( G ) is calculated based on the confocal feature of a confocal microprobe Raman system, showing one to two orders of amplification of Raman signal for adsorbed pyridine on roughened Pt surfaces. The involvement of charge transfer (CT) enhancement is inferred from the SERS intensity-potential profiles that are dependent on excitation lines. In general, the Pt surfaces with different roughness factors ( R ) can be divided into three categories: (1) the mildly roughened surface with R of 20–30 seems more adequate for the study of SERS mechnism including calculation of G ; (2) the moderately roughened surface with R ranging from 20 to 100, providing homogeneous morphologies, is suitable for investigating surface adsorption and reactions; (3) the highly roughened surface with R ranging from 100 to 300, with non-uniform morphologies, could only be used for investigating species having small Raman cross-sections such as hydrogen adsorption.

Can surface Raman spectroscopy be a general technique for surface science and electrochemistry

Surface-enhanced Raman spectroscopy has almost been restricted to the study of only three noble metals of Au, Ag and Cu for two decades. Recently, a new confocal Raman microscope and special surface pretreatments have allowed the acquisition of high-quality surface Raman spectra of organic and inorganic molecules adsorbed on bare Pt, Ni, Co, Fe, Pd, Rh, Ru and Si electrodes over a wide applied potential range for the first time. The present results demonstrate several advantages of in situ surface Raman spectroscopy that could probably make it a general technique widely used in surface science and electrochemistry.

In situ monitoring of Raman scattering and photoluminescence from silicon surfaces in HF aqueous solutions

In situ Raman spectra of SiHx, Si–F, and Si–Si vibrations from Si surfaces in HF aqueous solutions are obtained using a highly sensitive confocal microprobe Raman system. Electrochemical roughening pretreatment and laser-assisted roughening procedure enable good quality surface Raman spectra to be obtained. The surface Raman and photoluminescence spectra from the Si surface in the etching environment and the correlation of the two types of spectra are discussed. The Raman spectroscopy is shown to have high potential in serving as an important tool for in situ investigating of Si surface bonding during the etching process.

Initial Oxidation Processes on Hydrogenated Silicon Surfaces Studied by In Situ Raman Spectroscopy

The influence of the solution pH on H-terminated silicon surfaces in different electrolytes was investigated by in situ confocal Raman microscopy. This study provides Raman evidence that the initial oxidation of the hydrogenated silicon surface could occur by two paths. In the lower pH solution, the H-terminated silicon surface could he directly oxidized by the attack of OH - in the higher pH solution, the surface oxidation occurs in the second layer by the insertion of OH into the back bond of Si-H (Si-Si), in which an intermediate species of -O 3 SiH could he found, In the study of the influence of electrolytes, it was found that F ion could assist and accelerate the oxidation reaction, while the attack of OH ion is essential to the initial oxidation processes. By taking advantage of Raman Spectroscopy in the study of the low frequency region and analyzing the results from various samples. the assignment of the band located at about 629 cm 1 is discussed in detail and attributed to the vibrations of the silicon hydride and multiphonon structure.

Influence of annealing ambience on the formation of cobalt silicides

Abstract By using two sets of Raman systems with excitation lines of 514.5 and 632.8 nm, the influence of annealing ambience was investigated on the formation of cobalt silicides. The results show that a more uniform, compact and thermal stable cobalt silicide film can be formed in the hydrogen annealing ambience than that in the Ar annealing ambience. Two characteristic bands located at 305 and 325 cm −1 , which may be assigned to the CoSi and CoSi2, respectively, were found during the phase transition processes. The strong band which appeared at 325 cm −1 that can only be detected with the excitation line of 632.8 nm was found to be due to the resonant Raman effect.